As so-called front glass, generally laminated glass composed of two opposed plate-like glass sheets and an interlayer film for a laminated glass sandwiched between the glass sheets has been used for the front face of an automobile, an aircraft or the like.
In recent years, from a viewpoint of safety improvement, with respect to, for example, a front glass for an automobile, it has been highly required to display an instrument display such as a speed information, which is automotive driving data, as a head up display (HUD) in the same visible field as the front glass.
Various kinds of HUD mechanisms have been developed so far. For example, there is a HUD mechanism whose HUD display part is not in the front glass surface and by which the speed information and the like transmitted from a control unit is reflected to the front glass from a display unit on an instrumental panel to enable a driver to see the information at the same position as the front glass (that is, in the same visible field). For such a mechanism, since the laminated glass composing the front glass comprises two parallel glass sheets, there is a defective point that the instrument display reflected in the visible field of the driver is seen double.
To deal with such a problem, Patent Document 1 discloses a laminated glass using an interlayer film for a laminated glass with a wedge shape having a prescribed wedge angle.
Such a laminated glass enables a convergence of the instrument display reflected by one glass sheet and the instrument display reflected by the other glass sheet upon one point in the visible field of the driver by adjusting the wedge angle, and the laminated glass can solve the conventional problem that the instrument display is seen double, and the driver's visible field is never interfered.
However, such a laminated glass has a problem of inferior sound-insulating property in particular. Patent Document 1: Japanese Kokai Publication Hei-4-502525